The present invention relates to a variable reluctance resolver of a single-phase input and two-phase output type.
Heretofore, a rotation angle sensor which detects the rotation angle is known. The rotation angle sensor is widely used. For example, the rotation angle sensor is used for a wheel speed sensor, a handle rudder angle sensor, and the like in a power system of automobiles. The rotation angle sensor is also used for index tables of rotary drive units of robots, carrying apparatuses, and the like, automatic assembly machines, measurement machines, and the like, processing indexes of NC machine tools, specialized machines, and the like, for example. The rotation angle sensor used in a severe environment requires high environment resistance. For example, optical encoders or magnetic encoders which have been used heretofore for the rotation angle sensor are vulnerable to the influence of temperature changes and electromagnetic fields and have low environment resistance. A resolver is mentioned as the rotation angle sensor which realizes high environment resistance. Known as one of the resolvers is a variable reluctance resolver (hereinafter referred to as a VR resolver).
The VR resolver detects a rotation angle utilizing changes in magnetic resistance (reluctance) with the rotation of a resolver rotor. In a common VR resolver, an annular resolver stator has excitation windings and output windings which are wound in the shape of a coil. The excitation windings generate a magnetic field by the application of a voltage. The output windings output electric signals based on the magnetic field. Inside the resolver stator, a resolver rotor is disposed. The magnetic resistance in a magnetic path changes with the rotation of the resolver rotor. The electric signals output from the output winding change with the changes in the magnetic resistance. For example, by signal processing of the electric signals output from output coils by an external signal-processing circuit, the rotation speed or the rotation angle of the resolver rotor is calculated.
Various kinds of VR resolvers are referred to as “nX” for distinguishing them. “n” refers to the number of cycles of sine waves of a voltage output during one rotation of the resolver rotor in the output signal of VR resolver and is referred to as a shaft-multiple angle number n. For example, the VR resolver in which a 2-cycle sine wave is output during one rotation of the resolver rotor is referred o as “2X”. The shaft-multiple angle number n is determined by the shape of the resolver rotor. In general, when the number of slots of the resolver stator is defined as N, the VR resolver is constituted so that N=4n is established. For example, Patent Document 1 discloses a VR resolver having a 2X resolver rotor and a 8 slot resolver stator.
In the VR resolver, “nX” is increased for the purpose of detecting a rotation angle with high precision. According to the relationship of N=4n, in order to increase the “nX”, the number of stator slots needs to be increased. When the number of the stator slots is increased, a problem of an increase in the size of the VR resolver or an increase in cost arises.
As a method for increasing “nX” when the number of stator slots is in a fixed range (lower than 4n pieces), a configuration is known in which three coils (e.g., an excitation coil, a first-phase output coil, and a second-phase output coil) are provided from the inner circumferential surface to the outer circumferential surface of the stator slots. However, the outer diameter of the coils is different depending on the order of the layer around which the two output coils are wound. The phase or the impedance of the two output coils becomes unbalanced due to the difference in the outer diameter of the coils, and, as a result, an electrical error becomes large. The increase in the electrical error reduces the detection accuracy of the rotation angle. As an increase in the use of the VR resolver, high detection accuracy is required. Therefore, a small VR resolver in which the cost is low and the electrical error is small is desired.
The present invention has been made in view of the above-described circumstances. It is an object of the invention to provide a VR resolver capable of detecting a rotation angle with high precision with a limited number of stator slots.